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      1 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
      2 // Use of this source code is governed by a BSD-style license that can be
      3 // found in the LICENSE file.
      4 
      5 #include "sync/internal_api/public/base/node_ordinal.h"
      6 
      7 #include <algorithm>
      8 
      9 namespace syncer {
     10 
     11 NodeOrdinal Int64ToNodeOrdinal(int64 x) {
     12   uint64 y = static_cast<uint64>(x);
     13   y ^= 0x8000000000000000ULL;
     14   std::string bytes(NodeOrdinal::kMinLength, '\x00');
     15   if (y == 0) {
     16     // 0 is a special case since |bytes| must not be all zeros.
     17     bytes.push_back('\x80');
     18   } else {
     19     for (int i = 7; i >= 0; --i) {
     20       bytes[i] = static_cast<uint8>(y);
     21       y >>= 8;
     22     }
     23   }
     24   NodeOrdinal ordinal(bytes);
     25   DCHECK(ordinal.IsValid());
     26   return ordinal;
     27 }
     28 
     29 int64 NodeOrdinalToInt64(const NodeOrdinal& ordinal) {
     30   uint64 y = 0;
     31   const std::string& s = ordinal.ToInternalValue();
     32   size_t l = NodeOrdinal::kMinLength;
     33   if (s.length() < l) {
     34     NOTREACHED();
     35     l = s.length();
     36   }
     37   for (size_t i = 0; i < l; ++i) {
     38     const uint8 byte = s[l - i - 1];
     39     y |= static_cast<uint64>(byte) << (i * 8);
     40   }
     41   y ^= 0x8000000000000000ULL;
     42   // This is technically implementation-defined if y > INT64_MAX, so
     43   // we're assuming that we're on a twos-complement machine.
     44   return static_cast<int64>(y);
     45 }
     46 
     47 }  // namespace syncer
     48